Progress on the suppression of FM-to-AM modulations in SG-III laser facility

FM-to-AM modulations are harmful to output characteristics of large-scale laser facility. In SG-III laser facility, some key techniques have been employed to suppress FM-to-AM modulations. Firstly, phase modulator was arranged at the end of fiber laser injection system to avoid GVD and PMD in the SM fiber system. Secondly, a fiber-based polarization rotated filter was proposed to suppress FM-to-AM modulations independently on each beam. Finally, less wave plates were employed and liquid crystal modulators were coated for decreasing weak etalon effect in preamplifier system. The results indicated that it can reduce the modulation depth less than 10% at a modulation frequency of 2.488GHz in SG-III laser facility.